The present invention relates to thermal power plants and more particularly to methods and apparatus for improving power generation in thermal power plants.
The portion of power flow that results in a net transfer of energy in one direction (over a complete AC waveform cycle) is known as real power (or useful or active power). That portion of power flow that is due to stored energy in the load returning to the source in each cycle is known as reactive power. Apparent power is the vector sum of real and reactive power.
The power factor of an AC power system is defined as the ratio of real power to apparent power, and is a number between 0 and 1. Where the waveforms are purely sinusoidal, the power factor is the cosine of the phase angle (φ) between the current and voltage sinusoid waveforms. Power factor equals 1 when the voltage and current are in phase, and is zero when the current leads or lags the voltage by 90 degrees. If the load is purely reactive, then the voltage and current are 90 degrees out of phase and there is no net energy flow. Power factors are usually identified as “leading” or “lagging” to show the sign of the phase angle, where leading indicates a negative sign.
For two AC power systems transmitting the same amount of real power, the system with the lower power factor will have higher circulating currents due to energy that returns to the source from energy storage in the load. These higher currents in a power system will produce higher losses and reduce overall transmission efficiency. A lower power factor circuit will have a higher apparent power and higher losses for the same amount of real power transfer. Thus, it is desirable to maintain a high power factor in an AC power system.
Transmission operators, such as independent service operators (ISO's) and regional transmission operators (RSO's), compensate power generators for real power, which is given in megawatts (MWs), but typically do not compensate power generators for reactive power, which is given in mega volt-amperes reactive (MVar's). Reactive power, however, is necessary to maintain adequate voltage levels on a power grid. Without such voltage support, the transfer and distribution of real power would be adversely affected. For this reason, a transmission operator often requires a power generator to provide a certain amount of reactive power in order to connect to a power grid run by the transmission operator. Typically, the provision of such required reactive power reduces the amount of real power that a power generator could otherwise supply and reduces the power factor of the power generated by the power generator.
The present invention is directed to a method and apparatus for improving the supply of power from a thermal power generator.